We have recently used (P32)-8-N3cAMP to successfully photo-label the cAMP binding sites in three different cell systems. These are the human erythrocyte, slime mold (Dictyostelium Discoideum) and Sarcoma 37. After photo-labeling the cells are solubilized and electrophoresized on SDS polyacrylamide gels. The gels are stained for protein, dried on filter paper and autoradiographed. The autoradiograph allows determination of: (1) which proteins bind cAMP (2) the MW of these proteins and (3) the effects of the other compounds and stage of life cycle on the level and type of cAMP binding proteins that are present. In addition, the effect of cAMP and N3 cAMP on the phosphorylation of these membrane proteins by (gamma-P32)-ATP are being studied in a like manner. BIBLIOGRAPHIC REFERENCES: Haley, B. (1976), "Photoaffinity Labeling of Adenosine 3',5'-Cyclic Monophosphate Binding Sites", Methods in Enzymology, Jacoby & Wilchek Editors, (in press). Owens, J. R. and B. E. Haley (1976), "A Study of Adenosine 3',5'-Cyclic Monophosphate Binding Sites of Human Erythrocyte Membranes 8-Azidoadenosine-3',5'-Cyclic Monophosphate, A Photoaffinity Probe", J. of Supramolecular Structure, (in press).